A wireless power transmission device is a technology for wirelessly supplying power from a power feeding coil to a power receiving coil by utilizing an electromagnetic induction or a resonance of a magnetic field between a power feeding coil (primary coil) and a power receiving coil (secondary coil). In this wireless power transmission device, a soft magnetic core with a high magnetic permeability is used to increase the magnetic coupling between the feeding and receiving coils and to improve the power transmission efficiency.
However, when the above described wireless power transmission device is applied to a power feeding apparatus of a vehicle or the like, the power feeding coil will be placed on the ground. At this time, when a vehicle tire or the like runs on the power feeding coil, a load is also applied to the soft magnetic core mounted on the power feeding coil, thus, the requirements on the technology for protecting the soft magnetic core is increased. For example, in Patent Document 1, a structure is proposed which has a cover portion and a base portion that are integrally formed (up and down), wherein, the cover portion and the base portion, each being made of resin concrete, form a storage space in the inner part, wherein, at least an inner cylinder wall, the primary coil, a magnetic core and a low-shrinkage resin was contained in the storage space, wherein, the low-shrinkage resin filled mainly in the space between the coil conductive wires of the primary coil.